The reduction and oxidation behaviour of manganese oxides

Catalytic combustion of volatile organic compounds (VOCs: benzene and toluene) was studied over manganese oxide catalysts (Mn3O4, Mn2O3 and MnO2) and over the promoted manganese oxide catalysts with alkaline metal and alkaline earth metal. Their properties and performance were characterized by using the Brunauer Emmett Teller (BET), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The sequence of catalytic activity was as follows: Mn3O4 > Mn2O3 > MnO2, which was correlated with the oxygen mobility on the catalyst. Each addition of potassium (K), calcium (Ca) and magnesium (Mg) to Mn3O4 catalyst enhanced the catalytic activity of Mn3O4 catalyst. Accordingly, K, Ca and Mg seemed to act as promoters, and the promoting effect might be ascribed to the defect-oxide or a hydroxyl-like group. A mutual inhibitory effect was observed between benzene and toluene in the binary mixture. In addition, the order of catalytic activity with respect to VOC molecules for single compound is benzene > toluene, and the binary mixture showed the opposite order of toluene > benzene.

Catalytic combustion of VOCs over a series of manganese oxide catalysts

Three mesoporous manganese oxide catalysts (Mn 2 O 3 , Mn 3 O 4 and Mn x O y ) have been prepared, by means of the solution combustion synthesis, and tested for the total oxidation of volatile organic compounds (VOCs; ethylene, propylene, toluene and their mixture). The best results, in terms of the total oxidation of VOCs, were achieved with the Mn 3 O 4 catalyst, which showed the highest amount of electrophilic oxygen on the surface (O α -species). The most active powder catalyst was then deposited on a cordierite-type monolith through a novel direct synthesis and tested for the total oxidation of the VOCs mixture. The Mn 3 O 4 -based monolith exhibited high activity towards the total oxidation of VOCs, which is comparable to that obtained with powdered Mn 3 O 4 . The monolithic catalyst showed excellent catalytic activity for the total combustion of the mixture of VOCs (conversion to CO 2  = 99.2% ± 0.5) over a time-on-stream of 10 h at 310 °C and no deactivation occurred during this time span.

Mesoporous manganese oxides prepared by solution combustion synthesis as catalysts for the total oxidation of VOCs

Low-temperature NH 3 -SCR is an environmentally important reaction for the abatement of NO x from stationary sources. In recent years FeMnO x has attracted significant attention as a potential catalyst for this process, however its catalytic activity and SO 2 resistance require further improvement. In this contribution FeMnO x has been modified to examine the effect of ceria on catalytic activity and SO 2 resistance in the low temperature region. Preparation of catalysts via the citric acid method generate modified materials that exhibit enhanced NO turnover compared to FeMnO x . A reduction in NH 3 adsorption (NH 3 -TPD) and a suitable ratio between NO sites (NO-TPD) and chemisorbed surface oxygen (XPS) are beneficial for the promotion of fast-SCR. A comparative SO 2 resistance study of FeMnO x and Ce(12.5) showed that the latter exhibited improved stability in the presence of SO 2 , as indicated by the retention of pore volume (N 2 adsorption) and surface composition (XPS). In-situ DRIFTS demonstrated that chemisorbed N-containing species on Ce(12.5) were much more stable in the presence of SO 2 compared to FeMnO x , which resulted in the formation of significantly less metal sulphates and NH 4 HSO 4 .

Ceria modified FeMnO x -Enhanced performance and sulphur resistance for low-temperature SCR of NOx

Industrial-use catalysts usually encounter severe deactivation after long-term operation for catalytic oxidation of chlorinate volatile organic compounds (CVOCs), which becomes a “bottleneck” for large-scale application of catalytic combustion technology. In this work, typical acidic solid-supported catalysts of MnxCe1–xO2/HZSM-5 were investigated for the catalytic oxidation of chlorobenzene (CB). The activation energy (Ea), Bronsted and Lewis acidities, CB adsorption and activation behaviors, long-term stabilities, and surficial accumulation compounds (after aging) were studied using a range of analytical techniques, including XPS, H2-TPR, pyridine-IR, DRIFT, and O2-TP-Ms. Experimental results revealed that the Bronsted/Lewis (B/L) ratio of MnxCe1–xO2/HZSM-5 catalysts could be adjusted by ion exchange of H• (in HZSM-5) with Mnn+ (where the exchange with Ce4+ did not distinctly affect the acidity); the long-term aged catalysts could accumulate ca. 14 organic compounds at surface, including highly toxic te...

Catalytic Oxidation of Chlorobenzene over MnxCe1–xO2/HZSM-5 Catalysts: A Study with Practical Implications

Selective reduction of nitrobenzene has been measured on several kinds of Mn3O4 catalysts obtained by different methods of preparation. Attention is mainly given to the relationship between catalytic performance of different Mn3O4 materials and their redox behaviour. It was found that the catalyst having the most active redox behavior favoured the formation of highly reduced product (e.g. aniline etc) but, the catalyst having the least active redox behaviour showed poor catalytic activity. It seems that the catalytic as well as the redox behavior of Mn3O4 could be related to the Jahn-Teller effect.

Selective reduction of nitrobenzene to nitrosobenzene over different kinds of trimanganese tetroxide catalysts

Temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO), combined with differential thermal analysis (DTA) and FT-IR spectroscopy, were used to characterize trimanganese tetroxide catalysts. It was found that the redox behavior of Mn3O4 was considerably affected by different gas treatments, preparative condition and the addition of a promoter. A possible interpretation of two reduction peaks in the TPR profile of Mn3O4 has been suggested.

Redox behavior of trimanganese tetroxide catalysts

Influence of soluble aluminium on the state and surface properties of platinum in a series of reduced platinum/alumina catalysts

Influence of soluble aluminium on the thermal decomposition of praseodymium trinitrate/alumina and the study of the alumina support effect

The effect of competitive adsorbate, i.e., lactic acid, citric acid etc. on the adsorption equilibrium of H 2 PtCl 6 on η-Al 2 O 3 and the impregnation kinetics were studied. The obtained experimental results helped to explain, why with citric acid as a competitive adsorbate, a catalyst with Pt distributing within pelleted alumina in an egg-white (or eggyolk) zone may be resulted; while with lactic acid as a competitive adsorbate, Pt tends to be distributed in a broadened eggshell region or homogeneously.

Zhang Jiayu

Papers

Selective reduction of nitrobenzene to nitrosobenzene over different kinds of trimanganese tetroxide catalysts

Redox behavior of trimanganese tetroxide catalysts

Influence of soluble aluminium on the state and surface properties of platinum in a series of reduced platinum/alumina catalysts

Influence of soluble aluminium on the thermal decomposition of praseodymium trinitrate/alumina and the study of the alumina support effect

The Role of Competitive Adsorbate in the Impregnation of Platinum in Pelleted Alumina Support